Engineering topics

Momjian, E.

Publications and source records attributed to Momjian, E..

6 records

DOE OSTI2017

A 33 GHz Survey of Local Major Mergers: Estimating the Sizes of the Energetically Dominant Regions from High-resolution Measurements of the Radio Continuum

We present Very Large Array observations of the 33 GHz radio continuum emission from 22 local ultraluminous and luminous infrared (IR) galaxies (U/LIRGs). These observations have spatial (angular) resolutions of 30–720 pc (0.″07–0.″67) in a part of the spectrum that is likely to be optically thin. This allows us to estimate the size of the energetically dominant regions. We find half-light radii from 30 pc to 1.7 kpc. The 33 GHz flux density correlates well with the IR emission, and we take these sizes as indicative of the size of the region that produces most of the energy. Combining our 33 GHz sizes with unresolved measurements, we estimate the IR luminosity and star formation rate per area and the molecular gas surface and volume densities. These quantities span a wide range (4 dex) and include some of the highest values measured for any galaxy (e.g., Σ{sub SFR}{sup 33 GHz}⩽10{sup 4.1} M{sub ⊙} yr{sup −1} kpc{sup −2}). At least 13 sources appear Compton thick (N{sub H}{sup 33 GHz}⩾10{sup 24} cm{sup −2}). Consistent with previous work, contrasting these data with observations of normal disk galaxies suggests a nonlinear and likely multivalued relation between star formation rate and molecular gas surface density, though this result depends on the adopted CO-to-H{sub 2} conversion factor and the assumption that our 33 GHz sizes apply to the gas. Eleven sources appear to exceed the luminosity surface density predicted for starbursts supported by radiation pressure and supernova feedback; however, we note the need for more detailed observations of the inner disk structure. U/LIRGs with higher surface brightness exhibit stronger [C ii] 158 μm deficits, consistent with the suggestion that high energy densities drive this phenomenon.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

THE ZEEMAN EFFECT IN THE 44 GHZ CLASS I METHANOL MASER LINE TOWARD DR21(OH)

We report detection of the Zeeman effect in the 44 GHz Class I methanol maser line, toward the star-forming region DR21(OH). In a 219 Jy beam{sup −1} maser centered at an LSR velocity of 0.83 km s{sup −1}, we find a 20- σ detection of zB {sub los} = 53.5 ± 2.7 Hz. If 44 GHz methanol masers are excited at n ∼ 10{sup 7–8} cm{sup −3}, then the B versus n {sup 1/2} relation would imply, from comparison with Zeeman effect detections in the CN(1 − 0) line toward DR21(OH), that magnetic fields traced by 44 GHz methanol masers in DR21(OH) should be ∼10 mG. Combined with our detected zB {sub los} = 53.5 Hz, this would imply that the value of the 44 GHz methanol Zeeman splitting factor z is ∼5 Hz mG{sup −1}. Such small values of z would not be a surprise, as the methanol molecule is non-paramagnetic, like H{sub 2}O. Empirical attempts to determine z , as demonstrated, are important because there currently are no laboratory measurements or theoretically calculated values of z for the 44 GHz CH{sub 3}OH transition. Data from observations of a larger number of sources are needed to make such empirical determinations robust.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

New constraints on the molecular gas in the prototypical HyLIRGs BRI 1202-0725 and BRI 1335-0417

We present Karl G Jansky Very Large Array observations of CO(J=2→1) line emission and rest-frame 250 GHz continuum emission of the Hyper-Luminous IR Galaxies (HyLIRGs) BRI 1202–0725 (z = 4.69) and BRI 1335–0417 (z = 4.41), with an angular resolution as high as 0.″15. Our low-order CO observations delineate the cool molecular gas, the fuel for star formation in the systems, in unprecedented detail. For BRI 1202–0725, line emission is seen from both extreme starburst galaxies: the quasar host and the optically obscured submm galaxy (SMG), in addition to one of the Lyα emitting galaxies in the group. Line emission from the SMG shows an east–west extension of about 0.″6. For Lyα-2, the CO emission is detected at the same velocity as [C ii] and [N ii], indicating a total gas mass ∼4.0 × 10{sup 10} M {sub ⊙}. The CO emission from BRI 1335–0417 peaks at the nominal quasar position, with a prominent northern extension (∼1″, a possible tidal feature). The gas depletion timescales are ∼10{sup 7} years for the three HyLIRGs, consistent with extreme starbursts, while that of Lyα-2 may be consistent with main sequence galaxies. We interpret these sources as major star formation episodes in the formation of massive galaxies and supermassive black holes via gas-rich mergers in the early universe.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

THE ALFA ZOA DEEP SURVEY: FIRST RESULTS

The Arecibo L-band Feed Array Zone of Avoidance (ALFA ZOA) Deep Survey is the deepest and most sensitive blind H i survey undertaken in the ZOA. ALFA ZOA Deep will cover about 300 square degrees of sky behind the Galactic Plane in both the inner (30{sup ∘}⩽l⩽75{sup ∘};b⩽|2{sup ∘}|) and outer (175{sup ∘}⩽l⩽207{sup ∘};−2{sup ∘}⩽b⩽+1{sup ∘}) Galaxy, using the Arecibo Radio Telescope. First results from the survey have found 61 galaxies within a 15 square degree area centered on l=192{sup ∘} and b = −2°. The survey reached its expected sensitivity of rms = 1 mJy at 9 km s{sup −1} channel resolution, and is shown to be complete above integrated flux, F{sub Hi} = 0.5 Jy km s{sup −1}. The positional accuracy of the survey is 28″ and detections are found out to a recessional velocity of nearly 19,000 km s{sup −1}. The survey confirms the extent of the Orion and Abell 539 clusters behind the plane of the Milky Way and discovers expansive voids, at 10,000 and 18,000 km s{sup −1}. Twenty-six detections (43%) have a counterpart in the literature, but only two of these have known redshifts. Counterparts are 20% less common beyond v{sub hel} = 10,000 km s{sup −1} and 33% less common at extinctions higher than A{sub B} = 3.5 mag. The ALFA ZOA Deep survey is able to probe large scale structure beyond redshifts that even the most modern wide-angle surveys have been able to detect in the ZOA at any wavelength.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

HIGH-RESOLUTION RADIO CONTINUUM MEASUREMENTS OF THE NUCLEAR DISKS OF Arp 220

We present new Karl G. Jansky Very Large Array radio continuum images of the nuclei of Arp 220, the nearest ultra-luminous infrared galaxy. These new images have both the angular resolution to study the detailed morphologies of the two nuclei that power the galaxy merger and sensitivity to a wide range of spatial scales. At 33 GHz, we achieve a resolution of 0.''081 × 0.''063 (29.9 × 23.3 pc) and resolve the radio emission surrounding both nuclei. We conclude from the decomposition of the radio spectral energy distribution that a majority of the 33 GHz emission is synchrotron radiation. The spatial distributions of radio emission in both nuclei are well described by exponential profiles. These have deconvolved half-light radii (R {sub 50d}) of 51 and 35 pc for the eastern and western nuclei, respectively, and they match the number density profile of radio supernovae observed with very long baseline interferometry. This similarity might be due to the fast cooling of cosmic rays electrons caused by the presence of a strong (∼mG) magnetic field in this system. We estimate extremely high molecular gas surface densities of 2.2{sub −1.0}{sup +2.1}×10{sup 5} (east) and 4.5{sub −1.9}{sup +4.5}×10{sup 5} (west) M {sub ☉} pc{sup –2}, corresponding to total hydrogen column densities of N {sub H} = 2.7{sub −1.2}{sup +2.7}×10{sup 25} (east) and 5.6{sub −2.4}{sup +5.5}×10{sup 25} cm{sup –2} (west). The implied gas volume densities are similarly high, n{sub H{sub {sub 2}}}∼3.8{sub −1.6}{sup +3.8}×10{sup 4} (east) and ∼11{sub −4.5}{sup +12}×10{sup 4} cm{sup –3} (west). We also estimate very high luminosity surface densities of Σ{sub IR}∼4.2{sub −0.7}{sup +1.6}×10{sup 13} (east) and Σ{sub IR}∼9.7{sub −2.4}{sup +3.7}×10{sup 13} (west) L{sub ⊙} kpc{sup −2}, and star formation rate surface densities of Σ{sub SFR} ∼ 10{sup 3.7} {sup ±} {sup 0.1} (east) and Σ{sub SFR} ∼ 10{sup 4.1} {sup ±} {sup 0.1}(west) M {sub ☉} yr{sup –1}kpc{sup –2}. These values, especially for the western nucleus are, to our knowledge, the highest luminosity surface densities and star formation rate surface densities measured for any star-forming system. Despite these high values, the nuclei appear to lie below the dusty Eddington limit in which radiation pressure is balanced only by self-gravity. The small measured sizes also imply that at wavelengths shorter than λ = 1 mm, dust absorption effects must play an important role in the observed light distribution while below 5 GHz free-free absorption contributes substantial opacity. According to these calculations, the nuclei of Arp 220 are only transparent in the frequency range ∼5-350 GHz. Our results offer no clear evidence that an active galactic nucleus dominates the emission from either nucleus at 33 GHz.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2000

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export control compliance↗